The use of metal plates and screws to immobilize bone fragments dates back to the nineteenth century. Because of problems with infection and technical failures, however, the concept was not widely accepted. Bone plating for major long bones using the principle of axial compression was reintroduced with a great degree of success in the 1940s. I. R. Munroe, "The Luhr Fixation System For The Craniofacial Skeleton", 16 Clinics In Plastic Surgery, 41 (January 1989). Luhr and others started to use metal plates and screws in mandibular fractures in the late 1960s. Rigid fixation of facial skeletal fractures and osteotomies was started approximately a decade later, but was not widely accepted in North America. More recently, however, a rapid expansion of utilization of plates and screws for fractures, osteotomies and reconstruction of the entire craniofacial skeleton has occurred.
There are numerous bone plating systems on the market from a great number of orthopedic and maxillofacial companies throughout the world that enable surgical repair of facial bone fractures involving the frontal bones, the cranium, the orbital regions, the nose, the maxilla (upper jaw), and the mandible (lower jaw), etc. Many of these systems are constructed by laser cutting. The precision of compression and non-compression of bone plating systems is thus extraordinary.
Because of the influence of general orthopedics on facial bone surgery, early on, relatively large plates and screws were developed for rigid fixation of mandibular and maxillary fractures and osteotomies. Extremity
fractures involve strong bones that are exposed to remarkable muscle traction and compression forces and require larger plates that can withstand these forces until bone healing is complete. The very complex craniofacial skeleton, however, shows numerous areas of thin bones that are not exposed to any remarkable muscle actions and therefore do not need such strong and relatively large plates. This analysis has led to the development of "mini" or "micro" plates and screws of remarkably smaller dimension as compared to the plating systems used with bones of the extremities. Luhr, H. G., "Indications for Use of a Microsystem for Internal Fixation in Craniofacial Surgery," 1 The Journal of Craniofacial Surgery 35 (January 1990). Recently, mesh systems have also been developed for bridging bony defects. PA1 1. The plates and screws consist of the cobalt chromium molybdenum alloy vitallium (Howmedica, Inc.). Vitallium combines the property of high resistance to corrosion with optimal mechanical strength. PA1 2. The systems are designed to provide automatic axial compression to the fracture or osteotomy line (as well as to bone grafts). This is provided by means of eccentric plate holes and screws with conical screw heads. This automatic axial compression provides optimal reduction and maximum stability. PA1 3. The systems employ self-tapping screws. These shorten the duration of surgery and provide firm anchorage of the screws even in small bones. PA1 4. Each of the systems consists of specially designed implants and instruments for that system. These are clearly arranged in sterilized boxes. The various implants have been designed to meet the needs of the maxillofacial surgeon; therefore, a wide variety of plates and screws are available to allow for rigid skeletal fixation in all areas of the craniomaxillofacial surgery.
One of the most commonly used plating system developed to date is the Luhr system manufactured by Howmedica, Inc. The use of mandibular compression screw plates for the repair of mandibular fractures was first published by Luhr in 1968. Luhr, H. G., "Zur Stabilen Osteosynthese Bei Unterkieferfrakturne", Dtsh. Zahnarztl Z 23:754 (1968). Subsequently, based on the original concept by Luhr, several complete systems have been developed for use in all the various situations encountered in trauma and reconstructive surgery of the facial skeleton.
These systems include (1) the mandibular compression-screw system ("MCS") for the treatment of mandibular fractures (particularly designed for the intraoral approach); (2) the mini-compression system for the treatment of mid-face fractures, for reconstructive surgery of the facial skeleton and the skull, and for orthognathic surgery; (3) the mandibular reconstruction system ("MRS") for the reconstruction of mandibular defects, including condyle replacement; and (4) the micro-Luhr system. Luhr, H. G., "Vitallium Luhr Systems For Reconstructive Surgery Of The Facial Skeleton", The Otolaryngologic Clinics of North America, 573 (August, 1987). Other systems include the Wurzberg system marketed by Walter Lorenz and a new system being developed by Micro-Aire.
The main characteristics of the Luhr systems are as follows:
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Regardless of the plate system used, the plate must be contoured to lay passively against the underlying bone surfaces. To facilitate plate contouring, templates made of soft malleable tin alloy are available. These templates can easily be adapted to any individual bone surface merely by application of light finger pressure. The actual bone plate is then contoured on an instrument table reduplicating the individual shape of the template.
Therefore, even though the plating systems themselves are manufactured with extremely precise tolerances, a major element of imprecision remains for those surgeons who repair facial fractures and do orthognathic surgery or reconstructive procedures repositioning the facial skeletal structures to improve esthetics or function. When the osteotomy, fracture or bone graft is placed into appropriate position, the bone plate has to be manually bent to the contour of the new anatomy of the osteotomy, bone graft or fracture site. This manual manipulation creates a substantial element of imprecision even with the use of templates.
Maladapted bone plates lead to inappropriate bone contour, irritation of the overlying soft tissues, abnormal anatomy or contour defects and obviously either non-union, malunion or unaesthetic result. Importantly, after manual bending, the imprecision builds "memory" into the bone plate as the plate retains forces that would tend to inappropriately cause delayed movement of the bony segments. More precise contouring of the plate would decrease this phenomenon add lead to more accurate postoperative osseous positioning.
It would therefore be desirable to develop an apparatus and method to minimize the element of imprecision in contouring bone plates to be used in rigid fixation.